The regulation of what is termed voluntary motor activity most certainly involves to some degree, reciprocal interactions between the cerebral cortex and the cerebellum. Also it is reasonable to assume based upon the density and diversity of the known projections from the cerebral cortex to the basilar pontine nuclei (BPN), and the existence of a singular outflow system leading from the BPN to the cerebellum, that a principal component in those reciprocal connections which link the cortex and cerebellum is the cortico-ponto-cerebellar system. Although it has been proposed that the information transmitted from the cortex to the cerebellum via an obligatory synapse in the BPN represents a "copy" of those signals sent from the cortex to the spinal cord and other brainstem centers, relatively little hard physiological data exists concerning the actual functional operations performed by the system in general and the BPN in particular. Because of an interest in the control of voluntary motor behavior, the obvious involvement of such systems in a wide variety of neurological disorders ranging from developmental insults (cerebral palsy) to cerebral stroke, and the paucity of existing information on the functional parameters of the cortico-ponto-cerebellar system, we have chosen to undertake a variety of correlated anatomical and physiological studies focused on the organization of the adult BPN as well as the normal development of this region and its plastic or compensatory response to injury. Previous work from our laboratory has been heavily weighted in favor of the collection of anatomical data and now, with this foundation to build upon, we have proposed a more even balance of anatomical and physiological studies designed to clarify (1) synaptic circuitry in the BPN regarding the recently confirmed ascending spinal and brainstem inputs to the pontine nuclei, (2) the existence of pontine intrinsic neurons, (3) the participation of certain neurotransmitter agents in BPN circuitry, and (4) the potential for neonatal plasticity in the cerebellopontine system and interactions between pontine afferents and their target pontine neurons which might be important developmental regulatory factors.